A comparative study on combustion of sunflower shells in bubbling and swirling fluidized-bed combustors with a cone-shaped bed

This paper compares the combustion and emission performance between the bubbling and swirling fluidized-bed combustors (FBCs) fired with sunflower shells. Morphology and thermogravimetric characteristics of this biomass fuel were investigated prior to combustion tests. In both case studies, trials were performed at two fuel feed rates, 60 kg/h and 45 kg/h, while ranging excess air from 20% to 80% at fixed combustor load. Temperature and gas concentrations (O2, CO, CxHy as CH4, and NO) were measured along axial and radial directions in both reactors, as well as at their stacks. The radial and axial temperature profiles in the two FBCs were found to be rather uniform, whereas hydrodynamics and operating conditions had apparent effects on the emission performance of the combustors. Compared to the bubbling FBC, the swirling FBC ensured a more intensive fuel burnout rate in the bed, which resulted in higher NO emission from this combustor at identical operating conditions. Excess air of ∼55% seems to be optimal to ensure high combustion efficiency (∼99%) and acceptable CO, CxHy and NO emissions of both combustors. At the optimal operating conditions, the emissions of both FBCs were quite similar. As follows from analysis of the radial and axial gas concentration profiles, the swirling FBC with its highly intensive burnout rate in the bottom region can be designed with a noticeably smaller height compared to the bubbling fluidized-bed combustor.